. >> the reports of involvement by her husband and brother-in-law came as an absolute shock to them all. >> and in dagestan, the suspect's mother is adamant that her sons are innocent. >> what happened is a terrible thing, but i know that my kids have nothing to do with this. i know it. i am mother. >> joining us now from boston is nbc news national investigative correspondent michael isikoff. and frank silufo, director of the homeland security policy institute at george washington university. good afternoon, to both of you. mike, as the investigations continue both here and oversea, we understand that investigators are confident these brothers acted alone. even as their family members express utter bafflement. what are we learning about the larger case against these suspects? >> reporter: well first of all, this is looking, martin, more and more like a case of self-radicalization. now, nothing is conclusive and, you know, we're far from the end of this investigation right now. >> of course. of course. >> reporter: but the preliminary indicators, first, you have tsarnaev saying the two